The Shuttle Radar Topography
Mission instrument consisted
of three sections. The main antenna was located in the payload
bay of Space Shuttle Endeavour, the mast was connected to the main
antenna truss, and an outboard antenna was connected to the end of
the mast.

In order to gather topographic (elevation) data of Earth's surface, SRTM used the technique of interferometry. In interferometry, two images are taken from different vantage points of the same area. The slight difference in the two images allows scientists to determine the height of the surface.

When two interferometric radar data sets are combined (or "interfered") the first product made is called an interferogram.

(Portion of SIR-C interferogram of Fort Irwin, California)

To get two images from different vantage points, a main antenna was installed in Space Shuttle Endeavour's cargo bay. The main antenna both transmitted and received radar signals.

Once the shuttle was in space, a mast was deployed from a canister that was attached to the main antenna truss. The mast extended out 60 meters (200 feet).

At the end of the mast, an outboard antenna acted as the second vantage point and received radar signals.